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Experimental and Theoretical Studies of the Electrothermal Instability in a Nonequilibrium Plasma


Gilpin, Robert Ridgeway (1968) Experimental and Theoretical Studies of the Electrothermal Instability in a Nonequilibrium Plasma. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/H7BQ-RD31.


Experimental and theoretical studies have been made of the electrothermal waves occurring in a nonequilibrium MHD plasma. These waves are caused by an instability that occurs when a plasma having a dependence of conductivity on current density is subjected to crossed electric and magnetic fields. Theoretically, these waves were studied by developing and solving the equations of a steady, one-dimensional nonuniformity in electron density. From these nonlinear equations, predictions of the maximum amplitude and of the half width of steady waves could be obtained. Experimentally, the waves were studied in a nonequilibrium discharge produced in a potassium-seeded argon plasma at 2000°K and 1 atm. pressure. The behavior of such a discharge with four different configurations of electrodes was determined from photographs, photomultiplier measurements, and voltage probes. These four configurations were chosen to produce steady waves, to check the stability of steady waves, and to observe the manifestation of the waves in a MHD generator or accelerator configuration.

Steady, one-dimensional waves were found to exist in a number of situations, and where they existed, their characteristics agreed with the predictions of the steady theory. Some extensions of this theory were necessary, however, to describe the transient phenomena occurring in the inlet region of a discharge transverse to the gas flow. It was also found that in a discharge away from the stabilizing effect of the electrodes, steady waves became unstable for large Hall parameters. Methods of prediction of the effective electrical conductivity and Hall parameter of a plasma with nonuniformities caused by the electrothermal waves were also studied. Using these methods and the values of amplitude predicted by the steady theory, it was found that the measured decrease in transverse conductivity of a MHD device, 50 per cent at a Hall parameter of 5, could be accounted for in terms of the electrothermal instability.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:(Engineering Science and Physics)
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Engineering
Minor Option:Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Zukoski, Edward E.
Thesis Committee:
  • Unknown, Unknown
Defense Date:15 May 1968
Additional Information:Title varies in the 1968 Caltech commencement program: An Electrothermal Instability in a Nonequilibrium Plasma
Funding AgencyGrant Number
Daniel and Florence Guggenheim FoundationUNSPECIFIED
Air Force Office of Scientific Research (AFOSR)AF 49(638)-1285
Record Number:CaltechTHESIS:12072015-140402720
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9311
Deposited On:07 Dec 2015 22:45
Last Modified:02 Apr 2024 17:35

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